Method of forming a resilient contact structure

ABSTRACT

An interconnection contact structure assembly including an electronic component having a surface and a conductive contact carried by the electronic component and accessible at the surface. The contact structure includes an internal flexible elongate member having first and second ends and with the first end forming a first intimate bond to the surface of said conductive contact terminal without the use of a separate bonding material. An electrically conductive shell is provided and is formed of at least one layer of a conductive material enveloping the elongate member and forming a second intimate bond with at least a portion of the conductive contact terminal immediately adjacent the first intimate bond.

This application is a continuation of commonly-owned, copending U.S.patent application Ser. No. 08/340,144 filed Nov. 15, 1994 now U.S. Pat.No. 5,917,707 which is now U.S. Pat. No. 5,917,707 acontinuation-in-part of application Ser. No. 08/152,812 filed on Nov.16, 1993 now U.S. Pat. No. 5,476,211. This invention relates to aninterconnection contact structure, interposer, semiconductor assemblyand package using the same and method for fabricating the same.

BACKGROUND TO THE INVENTION

Heretofore many types of interconnections which have been provided foruse with the semiconductor devices have suffered from one or moredisadvantages limiting their broad application in the semiconductorindustry. There is therefore need for new and improved interconnectioncontact structure which overcomes such disadvantages so that it will beparticularly useful in semiconductor assemblies and packages and whichcan be broadly used throughout the semiconductor industry.

SUMMARY OF THE INVENTION

In general, it is an object of the present invention to provide acontact structure, interposer, a semiconductor assembly and packageusing the same and a method for fabricating the same which makes itpossible to use contact structures and particularly resilient contactstructures attached directly to active silicon devices.

Another object of the invention is to provide a structure, interposer,assembly and method which makes it possible to utilize under chipcapacitors to save in real estate.

Another object of the invention is to provide a structure, interposer,assembly and method of the above character which can be utilized forproviding more than one substrate precursor populated with card readysilicon on both sides which optionally can be interconnected withresilient contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments are set forthin the accompanying drawings.

FIG. 1 is a partial isometric view of a “skeleton and muscle” contactstructure incorporating the present invention which is in the form of afreestanding pin.

FIG. 2 is a partial isometric view similar to FIG. 1 but showing aresilient contact structure with a bend therein.

FIG. 3 is side elevational view in section showing a contact structurewith multiple bends and with a multiple layer shell.

FIG. 4 is a side elevational view in section of another embodiment of acontact structure incorporating the present invention in which the shellis provided with protrusions.

FIG. 5 is a side elevational view in section showing another embodimentof a contact structure incorporating the present invention in which thebend portion of the contact structure is shorted together by anelectrically conducting filled compliant elastomeric layer.

FIG. 6 is an isometric view in section of another contact structureincorporating the present invention utilized in conjunction withplated-through holes in a printed circuit board.

FIG. 7 is an isometric view in section of another embodiment of thecontact structure incorporating the present invention utilized inconjunction with plated-through holes in a printed circuit board inwhich a resilient contact structure is provided on one side of theprinted circuit board and in which the other side is provided with acontact structure that need not be resilient.

FIG. 8 is a side elevational view in section of another contactstructure incorporating the present invention and in which a pluralityof stems of the type described in FIG. 1 have been bridged together by asolder layer to form a solder column structure.

FIG. 9 is a side elevational isometric view in section of a contactstructure incorporating the present invention in which two redundantresilient compliant contact structures are provided per contactterminal.

FIG. 10 is a side elevational isometric view in section of anothercontact structure incorporating the present invention in which threeresilient contact structures are bridged together by a solder layer atthe uppermost and lowermost extremities while leaving the intermediatebend portions free of the solder so that a compliant solder column isprovided.

FIG. 11 is a side elevational view in section of another embodiment of acontact structure incorporating the present invention in which thecontact structure extends over an edge of the substrate to form a probecontact.

FIG. 12 is a side elevational view in section or another contactstructure incorporating the present invention which shows use of ashielded contact probe.

FIG. 13 is an isometric view partially in section of another contactstructure incorporating the present invention in which contactstructures can originate on one side of a contact carrier substrate suchas a printed circuit board and have one of the contacts extend through ahole to the other side and having the other contact structure extendingfrom the same side.

FIG. 14 is a combination side elevational and isometric view in sectionof another embodiment of the contact structure incorporating the presentinvention in which the probe is provided with a distal extremity whichhas a topography to minimize contact resistance when it is in engagementwith another contact terminal.

FIG. 15 is a view similar to FIG. 15 but showing use of a cantileveredcontact.

FIG. 16 is an isometric view partially in section of a contact structureincorporating the present invention in which the contact structures areformed into loops.

FIG. 17 is a view similar to FIG. 16 but showing two loops per contactand a solder layer bridged the loops to form a solder column.

FIG. 18 is an isometric view partially in section showing a contactstructure incorporating the present invention in which the contactstructures are arranged to form a fence which can serve as a dam for amassive solder column as for example one utilized as a thermalinterconnect.

FIG. 19 is an isometric view partially in section showing an interposerincorporating the present invention.

FIG. 20 is an isometric view partially in section showing a double-sidedinterposer.

FIG. 21 is an isometric view partially in section or another interposerincorporating the present invention with resilient contact structures onone side and solderable contacts provided on the other side.

FIG. 22 is an isometric view partially in section showing anotherembodiment of an interposer incorporating the present inventionutilizing double-sided resilient compliant contact structures andstandoffs.

FIG. 23 is an isometric view partially in section of an activesemiconductor assembly incorporating the present invention.

FIG. 24 is an isometric view partially in section showing staggeredcontact structures with alignment pins.

FIG. 25 is a side elevational view in section of a semiconductor packageincorporating the present invention showing a double-sided flip chipattachment.

FIG. 26 is a side elevational view in section of a semiconductor packageincorporating the present invention.

FIG. 27 is a side elevational view in section of another embodiment of asemiconductor package incorporating the present invention utilizingdemountable contact structures.

FIG. 28 is a side elevational view in section of another semiconductorpackage incorporating the present invention which utilizing resilientcontact structures demountably interconnected and plated through holes.

FIG. 29 is a side elevational view in section of another semiconductorpackage assembly incorporating the present invention utilizing latchingsprings.

FIG. 30 is a side elevational view in section of another semiconductorpackage incorporating the present invention utilizing alignment pins.

FIG. 31 is a side elevational view in section of another semiconductorpackage incorporating the present invention carrying a below-the-surfacecapacitor.

FIG. 32 is a side elevational view in section or another semiconductorpackage incorporating the present invention showing the mounting of aplurality of capacitors.

FIG. 33 is a side elevational view in section of another semiconductorpackage incorporating the present invention utilizing a decouplingcapacitor.

FIG. 34 is a side elevational view in section of another semiconductorpackage incorporating the present invention utilizing a motherboard.

FIG. 35 is a side elevational view in section of another semiconductorpackage incorporating the present invention utilizing an interposer.

FIG. 36 is an isometric view partially in section of a semiconductorpackage incorporating the present invention utilizing an interconnectionsubstrate.

FIG. 37 is a side elevational view of a semiconductor packageincorporating four layers of semiconductor devices in the form ofdouble-sided precursors.

FIG. 38 is a side elevational view in section of a semiconductor packageincorporating the present invention showing vertically stacked siliconchips.

DESCRIPTION OF PREFERRED EMBODIMENTS

In general the contact structure of the present invention is for usewith a device which incorporates an electronic component having asurface and a conductive contact pad thereon accessible from the surfaceof the electronic component and also having a surface. A conductive,flexible, elongate element is provided which has first and second ends.Means is provided for bonding the first end to the contact pad to form afirst intimate bond, with the second end being free. A conductive shellenvelops the flexible elongate element and at least a portion of thesurface of the contact pad immediately adjacent the means bonding thefirst end to the contact pad to provide a second intimate bond so thatthe bond strength between the contact pad and the conductive shell isgreater than the bond strength between the contact pad and the flexibleelongate element.

More particularly as shown in the drawings, the contact Structure 101 inFIG. 1 is for use for making contact to an electronic component 102which for example can be an active or passive semiconductor device or aplastic laminate, ceramic or silicon package carrying one or moresemiconductor devices. It also can be an interconnection component suchas a connector. Alternatively, it can be a production, test or burn-insocket for a semiconductor package or semiconductor device. In any eventthe electronic component 102, which also can be called a supportstructure, is utilized for carrying the contact structures 101. Theelectronic component is provided with one or more conductive contactpads 103 which typically lie in a plane on a surface 104 or accessiblefrom or which are through the surface 104 of the electronic component102 with the pads 103 being positioned at various locations and lying invarious planes at various angles. The pads 103 can be peripherallypositioned at the perimeter of the electronic component 102. They alsocan be placed in an area array, near an edge or in a central linepad-out or a combination of the above well known to those skilled in theart. Typically each pad 103 has an electrical function dedicated to it.In certain applications, the contact pads 103 may in fact lie indifferent planes, or overlie the edge of a component. The contact pads103 can be of any desired geometry. For example they can be circular orrectangular in plan and have exposed surfaces 105. The pads 103 by wayof example can have any dimension, but typically range from 2 to 50mils.

The contact structure 101 includes an elongate element 106 whichtypically is flexible because of its small diameter, the flexibilityintended for ease of shaping, and has first and second ends 107 and 108.It also can be called a core wire or “skeleton”. The elongate element106 is formed of a suitable conductive material such as gold, aluminumor copper with small amounts of other metals to obtain desired physicalproperties as for example beryllium, cadmium, silicon and magnesium. Inaddition, metals or alloys such as metals of the platinum group, can beutilized. Alternatively, lead, tin, indium or their alloys can be usedto form the elongate element. The elongate element 106 can have adiameter ranging from 0.25 to 10 mils with a preferred diameter of 0.5to 3 mils. The elongate element 106 can have any desired length buttypically it would have a length commensurate with its use inconjunction with small geometry semiconductor devices and packagingwould range from 10 mils to 500 mils.

Means is provided for forming a first intimate bond between the firstend 107 of the conductive elongate element 106 and one of the contactpads 103. Any suitable means can be utilized for making this connection.For example, a wire bond utilizing a capillary tube (not shown) havingthe elongate element 106 extending therethrough and typically having aball provided on the first end is brought into engagement with the pad103 whereby upon the application of pressure and temperature orultrasonic energy, a wire bond, typically a ball-type bond 111 is formedconnecting the first end 107 of the elongate element 106 to the pad 103.After the desired wire bond 111 has been formed, the capillary tube canbe raised to permit a desired length of the elongate element 106 toextend from the capillary tube and a cut can be made by locally meltingthe wire to sever the elongate element 106 and to cause a ball 112 to beformed on the second end 108 of the elongate element 106 and also toprovide a corresponding ball on the remaining length of elongate element106 in the capillary tube so that the next contact structure can be madeutilizing the same wire bonding machine with the next pad if it isdesired to make a ball-type bond connection. Alternatively, wedge-typebonds can be utilized.

In accordance with the present invention, a conductive shell 116 whichalso can be called “muscle” which covers the “skeleton”, is formed overthe elongate element 106 and completely surrounds the same as well asthe surface area 105 of the contact pad 103 which immediately surroundsthe wire bond 111 and preferably extends over the contact pad 103 toform a second intimate bond to the contact pad 103 by direct adhesion tothe entire exposed surface of the contact pad. Thus, the contactstructure 101 is anchored to the contact paid 103 by the first andsecond intimate bonds. The shell 116 in addition to having conductiveproperties also has other mechanical properties desired for thecomposite contact structure 101 as hereinafter explained.

The shell 116 is formed of a material to provide desired mechanicalproperties for the contact structure. The material of the shell shouldprincipally be of a material which has a high yield strength with atleast thirty thousand pounds per square inch. In connection with thepresent contact structure, the adhesion strength between the contactstructure 101 and the contact pad 103 is principally or predominantlydue, i.e., more than 50%, to the adhesion between the shell 116 and thecontact pad 103. The shell 116 typically has a wall thickness rangingfrom 0.20 mils to 20 mils and preferably has a wall thickness of 0.25 to10 mils. The shell 116 in accordance with the present invention adheresto the elongate element or skeleton 106 along its length and to thesurface or the pad 103 to provide in effect a unitary structure.Typically the hardness of the elongate element or skeleton 106 is lessthan that of the material on the shell. When it is desired to have acontact structure which deforms plastically, the shell 116 can be formedof a conductive material such as copper or solder, exemplified bylead-tin solder. When it is desired to have the shell 116 have springproperties, nickel, iron, cobalt or an alloy thereof can be used. Othermaterials which would render desirable properties to the shell 116 incertain applications are copper, nickel, cobalt, tin, boron,phosphorous, chromium, tungsten, molybdenum, bismuth, indium, cesium,antimony, gold, silver, rhodium, palladium, platinum, ruthenium andtheir alloys. Typically, the top layer comprising the shell, if it isrequired, consists of gold, silver, metals or alloys of metals of theplatinum group or various solder alloys. Certain materials, as forexample nickel, when electroplated under certain bath conditions, ontothe elongate element 106 will form internal compressive stresses toincrease the stress required to deform or break a resulting contactstructure 101. Certain materials such as nickel can provide a tensilestrength in excess of 80,000 lbs. per square inch.

The shell or “muscle” 116, made of one or more of the materials listedabove, typically can be formed onto the flexible elongate element or“skeleton” by the use of a conventional aqueous plating technique. Theshell 116 also can be provided by enveloping the elongate element 106using physical or chemical vapor deposition techniques utilized inconventional thin film processes and can include decomposition processesusing gaseous, liquid or solid precursors as well as evaporating orsputtering.

Thus it can be seen that the final properties desired for the contactstructure 101 can be readily designed into the contact structure 101comprising the skeleton 106 and the muscle 116 while achieving thedesired conductivity and other physical properties as for example adesired pull strength or adhesion for the first and second intimatebonds formed with the contact pad 103. The shell or muscle 116 whichcompletely envelops the flexible elongate element or skeleton 106overlies the contact pad 103 to form the second adhesive bond therewith.

In connection with the foregoing description, a single contact structure101 has been described. However it should be appreciated that manyhundreds of contact structures 101 can be created at the same timeduring the plating or deposition process on a single electroniccomponent or a plurality of such electronic components.

As can be seen, the shell 116 has a substantial uniform thicknessthroughout its length and in overlying the contact pad 103. Thethickness of the shell can alternatively vary by adjusting the nature ofthe layers comprising the shell or by varying deposition parameters. Theuppermost free extremity of the contact structure or pin 101 is onlyslightly larger to reflect the shape of the ball 112 typically providedon the second or free end of the elongate element 106 below the shell116. It should be appreciated that if desired, the ball 112 provided onthe second end of the elongate element 106 can be eliminated if desiredby using means cutting the continuous wire other than by the use of amelting technique. Thus the second end would be in the form of asubstantially cylindrical member having the same diameter as thediameter of the elongate element 106.

When it is desired to provide resiliency in a contact structure, thecontact structure 121 shown in FIG. 2 can be utilized. The contactstructure 121 includes a flexible elongate conductive element 122 whichcan be formed of the same conductive materials as the elongate element106 shown in FIG. 1. It is provided with first and second ends 123 and124 with a ball-type bond 126 formed on the first end 123 and adhered tothe pad 103 in the same manner as the ball bond 111. While the elongateconductive element 122 is being discharged through the capillary of thewire bonder, a cantilever or cantilever portion 122 a forms a bend.Thus, there is provided a bend which forms at least one cantileveredportion. Such a cantilevered portion can give resilient capabilities tothe contact structure 121 as hereinafter provided. After the bend 122 ahas been formed, a tip 127 is provided on the second end 124 by anappropriate severing operation. A shell 131 is thereafter formed on theelongate conductive element 122 in the same manner as the shell 116hereinbefore described to encompass the elongate conductive element 122and being adherent to and overlying the contact pad 103. It can beappreciated that a variety of shapes other than the exact one depictedin FIG. 2 can be utilized.

In order to impart additional strength to the contract structure 121,the shell 131 principally is formed of a material which will impart highyield strengthening properties, as for example a strong, conductive,hard material to a thickness as hereinbefore described in connectionwith FIG. 1. Such a conductive material can be selected from the groupof nickel, cobalt, iron, phosphorous, boron, copper, tungsten,molybdenum, rhodium, chromium, ruthenium, lead, tin and their alloys.

In the contact structure 121 it can be seen that the elongate conductiveelement 122 defines the trajectory or shape of the contact structure 121wherein the shell 131 defines the mechanical and physical properties ofthe contact structure as for example the springiness or resilience ofthe contact structure as well as the ability to provide a low resistancespring-loaded contact through a noble top layer. It can be seen byviewing FIG. 2 that as the second or free end of the contact structure121 is moved upwardly and downwardly, the cantilever or bend 122 a canreadily accommodate the changes in position of the second free end andwill spring back and provide a substantially constant yieldable forcewithin the range of a given-design attempting to return the second endof the contact structure 121 to its original position. The spring shapecan be designed to respond in a resilient manner to a force directed atany angle relative to the surface of electronic components 102.

Another contact structure 136 incorporating the present invention isshown in FIG. 3 in which a flexible elongate conductive element 137 hasbeen provided which has two bends, 137 a and 137 b formed therein andwith a ball bond 138 at one end and a ball 139 at the other end. As canbe seen, the bends 137 a and 137 b face in opposite directions. A shell141 of the type hereinbefore described has been provided. However, it isformed of a first or inner layer 142 and a second or outer layer 143. Byway of example, the first or inner layer 142 could be in the form of acoating of nickel or a nickel alloy of a suitable thickness as forexample 1 to 3 mils to provide the desired springiness and/or yieldstrength for the contact structure. Assuming that it is desired toprovide a particular outer surface for the contact structure 136, thesecond or outer layer 143 can be formed of gold or other suitableconductive material. In certain applications it may be desired toutilize the first or inner layer 142 as a barrier layer as for exampleto utilize the contact structure 136 with a solder contact to preventthe interaction of gold with solder. In such applications it may bedesired to coat the flexible elongate conductive element 137 with a thinlayer or copper or nickel followed by 1 to 1.5 mils of solder such as alead-tin alloy. Thus it can be seen that by forming the shell of morethan two layers, it is possible to obtain additional desirable featuresfor the contact structure. It also should be appreciated that ifdesired, additional layers can be provided as a part of the shell incertain applications.

Another contact structure 146 incorporating the present invention isshown in FIG. 4 in which a flexible elongate conductive element 147 isprovided with an outwardly facing bend 147 a in which a shell 148 hasbeen provided which envelops the flexible elongate conductive member147. However in this case, the shell 148 has been formed in such amanner so as to provide microprotrusions 149 on the outer surfacethereof spaced longitudinally along the length of the shell. Theseprotrusions or irregularities can be created in a number of ways as forexample by adjusting the processing conditions in the plating bath tocause sharp nodules to be formed in the shell 148.

Another contact structure incorporating the present invention is acontact structure 151 shown in FIG. 5 which includes a flexible elongateelement 152 having a shell 153 thereon which is provided with acantilever portion in the form of a U-shaped bend 152 a. To reduce theelectrical inductance which is created during the conduction ofelectrical current in the contact structure 151, the bend 152 isimbedded in an electrically conductive compliant polymer mass 154 of asuitable type such as silicon rubber filled with silver particles. Thecompliant electrically conductive elastomer 154 does not substantiallyrestrain movement of the resilient portion 152 a of the contactstructure 151. The conductivity of the material 154 typically can rangefrom 10⁻² to 10⁻⁶ ohm centimeters.

In FIG. 6, contact structures 155 similar to the type shown in FIG. 2are utilized in connection with an electronic component in the form of aconventional printed circuit board 156. The printed circuit board 156 isprovided with conventional vertical via conductors in the form ofplated-through holes 157 in which a plating structure 158 extendsthrough the holes 157 and forms annular rings 159 provided on theopposite surfaces of the board 156 so that electrical contact can bemade from one side of the board 156 to the other side of the board. Asshown, a contact structure 155 is provided on each side of the printedcircuit board 156 and is in contact with the plating structure 158forming the rings 159 which functions as a contact pad. Thus, thecontact structure 155 serves to form an electrical connection betweencontact pads on two electronic components facing each side of thecircuit board 156 provided on opposite sides of the plated-through hole157. It can be seen that the shell 131 provided as a part of the contactstructure 155 also extends through the plated-through hole 157 and isdisposed on the annular plating 158 provided on both sides of the platedthrough hole 157. Such a construction can be readily manufactured merelyby flipping the printed circuit board 156 from one side to the otherduring the process of attachment of the flexible elongate elements ofthe contact structure 155. As hereinafter described, this type ofconstruction can be utilized in conjunction with an interposer. Byutilizing the contact structures 155, compliance capabilities areprovided on opposite sides of the printed circuit board making possibleface-to-face connections between matching pads on electronic componentsby an interposer carrying the contact structures shown in FIG. 6.

When compliance is only required on one side, a construction such asthat shown in FIG. 7 can be utilized. In this embodiment, the contactstructure 161 provided on one side as for example the bottom side asviewed in FIG. 7 includes a flexible elongate element 162 which has afirst bond 163 in the form of a ball bond secured to the metallization158. The contact structure 161 forms a loop which extends across thehole 157 and is bonded to the other side of the ring 159 by suitablemeans such as a second bond 164 in the form of a wedge bond of is a typewell known to those skilled in the art and use of wire bonding machinesutilized in the semiconductor industry. The flexible elongate element162 is covered by a shell 166 of a material of a type hereinbeforedescribed. It also should be appreciated that since compliance is notneeded on the lower side of the electronic component 156 that thecontact structure 161 can be replaced by a straight pin-like contactstructure 101 as shown in FIG. 1.

In FIG. 8 there is shown another embodiment of a contact structure 171incorporating the present invention which i6 used to form a soldercolumn. The contact structure 171 is a composite contact structure andis comprised of three “skeleton” structures 106 of the type shown inFIG. 1 which are spaced substantially 120° apart and which are mountedon a single contact pad 103. After the three “skeleton” structures 106have been made, a first continuous shell layer 172 is deposited ontoelongate “skeletons” 106 and the conductive pad 103 to form contactstructures like contact structures 101. This structure is then completedinto a solder post by placing solder layer 174 therebetween. The soldercan be of a suitable type such as an alloy of lead and tin which bridgesbetween the pin-like contact structures and the coated surface ofterminal 103 to form the solder post contact structure 171. Depending onthe use of the solder post, the solder post can be various sizes as forexample it can have a diameter range from 10 to 50 mils with a typicaldiameter being from 10 to 20 mils. These solder posts can have asuitable height as for example 10 to 200 mils with a typical height of20-150 mils. As explained hereinbefore, the balls 112 of the contactstructures 101 can be eliminated if desired by the use of a non-meltingsevering operation.

In FIG. 9 there is shown a composite contact structure 176 which isprovided with two contact structures 177 mounted on a single pad 103with cantilevered portions 177 a and 177 b facing in opposite directionsto provide two redundant resilient compliant contact structures 177 foreach contact pad.

Another composite contact structure 181 is shown in FIG. 10 in whichsolder 182 is provided for bridging the upper and lower extremities ofthe contact structures 177 but not bridging the portions of the contactstructures 121 having bends 177 a and 177 b therein so that complianceis still retained. With such an arrangement, it also should beappreciated that three of such contact structures 177 can be providedspaced 120° apart with solder 182 therebetween and that the contactstructures 177 do not have to be resilient in order to form a solderablecontact.

Another embodiment of a contact structure incorporating the presentinvention is shown in FIG. 11 in which a probe-like contact structure186 is shown. It includes a flexible elongate element 187 which has oneend secured to the contact pad 103. The flexible elongate element 187 isprovided with a bent cantilevered portion 187 a. Another portion 187 bextends downwardly over one edge of the electronic component 102, oralternatively through a feed-through hole of the type hereinbeforedescribed and is bonded by suitable means such as a wedge bond to asacrificial metal layer 188 as for example an aluminum layer which issecured to the component 102 by a thick photoresist 189 which serves asa standoff. After that step has been completed, the aluminum layer 188can be sacrificed by etching it away with a suitable etch such as sodiumhydroxide. The flexible elongate element 187 can then be coated in themanner hereinbefore described with a shell 190 formed of a nickel cobaltalloy or other suitable material as hereinbefore described to provide afree standing spring-like contact structure 186 which has its curveddistal extremity disposed in a position below the component 102. Thematerial utilized in the shell 190 makes it possible to control thedeflection characteristics of the free extremity of the probe contactstructure. Alternatively, the shell 190 can be completed first afterwhich the sacrificial layer 188 can be etched away. Alternatively, itshould also be appreciated that the bond of the elongate member to theterminal 103 can be of a wedge type and the bond to the sacrificialstructure 188 can be a ball-type bond.

In FIG. 12 there is shown another probing contact structure 191 which isprovided with a flexible elongate element 192 that is bonded by a bond193 to the contact pad 103. As in the previous embodiment, the flexibleelongate element 192 is provided with a cantilever or bend 192 a and aportion 192 b. The portion 192 b extends over the edge 194 or through ahole provided in the component 102. A shell 195 is provided over theflexible elongate element 192. Additional layers are provided over theshell 194 and consist of a layer 196 formed of a dielectric materialwhich is followed by a metal layer 197. If layer 197 is grounded, thereis provided a probe contact structure 191 which provides a shieldedcontact with controlled impedance. Thus it is possible to use a probecontact structure 191 in systems where shielding is desirable ornecessary to improve electrical performance of the probing structure. Asshown in FIG. 12, the distalmost extremity of the probe contactstructure 191 can be left free of the dielectric layer 196 and the metallayer 197 so that direct contact can be made with another contact pad oranother structure.

In FIG. 13 there is shown another embodiment of a contact structure 201incorporating the present invention in which the electronic component202 in the form of printed circuit board can be utilized as aninterposer as hereinafter described. As in the previous embodiments, itis provided with a hole 203 having plating surrounding the hole 203 toprovide contact pads 204. The contact structure 201 is of the typehereinbefore described which has a portion 206 that extends upwardly onone side of the electronic component 202 and another portion 207 thatextends downwardly through the hole 203 to the other side of theelectronic component 202. The portion 207 is temporarily bonded to asacrificial substrate (not shown) which is removed by etching ashereinbefore described. With such a construction, it can be seen thatelectrical connections can be made from both sides of the electroniccomponent 202.

Another embodiment of a contact structure 211 incorporating the presentinvention is shown in FIG. 14 in which a sacrificial aluminum layer 212is utilized during construction. In the area where it is desired to forma contact pad on the aluminum layer 212, a plurality of negativeprojections or holes 213 are formed in the surface of the aluminum layer212. As shown, these negative projections or holes 213 can be in theform of inverted pyramids ending in apexes. The negative projections orholes 213 in the aluminum are then filled with a conducting material 214such as gold or rhodium 214. This is followed by a nickel layer 216 anda layer of gold 217. A flexible elongate conductive element 218 formedof a suitable material such as gold or aluminum is then bonded to thegold layer 217 by suitable means such as a bond 219. The flexibleelongate element 218 extends through a curve or bend 218 and then goesover one side of the electronic component 102 and extends over the topof the contact pad 103 and is bonded thereto in a suitable manner suchas by a bond 220. Thereafter a shell 221 formed of a spring alloymaterial of the type hereinbefore described is deposited over theflexible elongate element 218 and extends over the contact pad 103 andover the gold layer 217 to complete the contact structure. By anappropriate combination of the properties of the shell 221 and thetrajectory of the bond or curve 218, the desired resilience can beobtained.

During this plating procedure, the sacrificial aluminum layer 212 can becovered with a suitable resist in a manner well known to those skilledin the art. After the contact structure has been completed, the resistthen can be removed and the sacrificial aluminum layer 212 can bedissolved in the manner hereinbefore described to provide a contact pad224 at the free end of the contact structure 211. In this manner it canbe seen that a contact pad can be constructed with a controlled geometryas for example one having a plurality of sharp points which can applyhigh local pressure forces to contact another pad as for example analuminum pad on a semiconductor device to break any oxide present on thealuminum pad and to make good electrical contact therewith by causingdeformation of the aluminum pad around the sharp points. These highcontact forces can be created while applying a relatively low overallforce on the contact pad 224.

Still another contact structure incorporating the present invention isshown in FIG. 15 which shows a contact pad 227 carried by the free endof the contact structure 226. The contact pad 227 has a dependingmechanically shaped probe 228 carries at one end of a rectangularcontact pad 227. The contact pad 227 is constructed in a manner similarto the contact pad 224 and by way of example can be provided with anickel or rhodium tip or probe 228 and a layer 229 also formed of nickelor rhodium. The layer 229 is covered with another isolation layer 231 ofa nickel alloy which is covered with a gold layer 232. A flexibleelongate element 236 of a conductive material is connected to the pad103 by a bond 237 and extends over the edge of the semiconductorstructure 102 through a cantilever or bend 236 a and is bonded to thegold layer 232 in a suitable manner such as by a bond 238. The flexibleelongate element 236 as well as the bonds 237 and 238 are overplatedwith a shell 239. The shell 239 is of a strong alloy of the type ashereinbefore described and extends over the pad 103 and over the entiregold layer 232. With this type of a contact structure 226, it can beseen that a cantilevered probe 228 is provided which enhances theability to control the deflection versus load behavior of the contactstructure 226.

Another contact structure 241 incorporating the present invention isshown in FIG. 16. The contact structure as shown is bent into a loop.This is accomplished by taking a flexible elongate element 242 of aconductive material and bonding it to one side of the contact pad 103 ina suitable manner such as by ball bond 243 and then forming the flexibleelongate element into an upside down loop 242 a which is generally inthe form of a “U” and then attaching the other end of flexible elongateelement to the other side of the contact pad 243 by suitable means suchas a wedge bond 244. A shell 246 can then be formed on the flexibleelongate element 242 in the manner hereinbefore described which isdeposited over the bonds 244 and 246 and over the edges of the contactpad 103. In this way it is possible to provide a relatively rigidcontact structure 241. It should be appreciated that if desired, morethan one of the looped contact structures 241 can be provided on a pad103. For example, two of such structures can be provided which arespaced apart on the same contact pad 103.

Another contact structure 251 incorporating the present invention isshown in FIG. 17 and is comprised of two of the contact structures 241hereinbefore described in conjunction with FIG. 17 which have beenspaced apart and mounted on the same pad 103 and in which a solder layer252 is formed over the contact structures 241 and bridges the U-shapedspaces provided between the contact structures 241. In addition asshown, the solder can bridge the two separate contact structures 241 toprovide a unitary solder bump 253. It should be appreciated that ifdesired, the two contact structure 241 can be spaced far enough apart sothat the solder will not bridge between the two contact structure 241but will only bridge between the bridge formed in each of the contactstructures 241 to provide separate solder bumps on a pad 103.

Still another contact structure 256 is shown in FIG. 18 in which a largecontact pad 103 is provided on the semiconductor component 102 or otherelectronic component and in which a plurality of contact structures 241of the type hereinbefore described are placed around the outer perimeterof the pad 103. The bonding of the internal elongate element or skeletonis started with a ball bond 243 and successive loops are made with wedgebonds 244 therebetween to in effect form a rectangular fence enclosing avolume. The internal elongate element is then overcoated with a shell(not shown) of the type hereinbefore described. The rectangular fencethen can be filled with solder (not shown) to provide a freestandingsolder contact or a bump which can serve as a heat sink where that isdesired.

An interposer 301 is shown in FIG. 19 and includes a substrate 302having first and second planar surfaces 303 and 304. The substrate 302can have a suitable thickness as for example ranging from 5 to 200 milsand preferably has a thickness of 20 to 100 mils. The substrate 302 canbe formed of a suitable material such as a molded plastic which servesas an insulator and is provided with a plurality of spaced apart holes306 extending through the first surface 303 and a plurality of spacedapart holes 307 extending through the second surface 304. The holes 306and 307 can have any desired geometry in cross section as for examplecircular. As shown, the holes 306 and 307 are eccentric. Thus each ofthe holes 306 and 307 is provided with a straight sided wall portion 308which extends perpendicular to the surface through which it extends andcan include an inclined wall portion 309 which is inclined inwardly anddownwardly into the hole. As can be seen from FIG. 19, the holes 306 and307 are arranged in pairs in which the holes in each pair are offsetslightly with respect to each other and are interconnected by passage311 extending between the same so that in effect there is provided asingle hole extending through the substrate 302 with one portion of thehole on one side being offset with respect to the portion extendingthrough the other side of the substrate. Thus in effect there isprovided a composite hole 312 which can be plated in a conventionalmanner as for example as utilized with printed circuit boards forproviding a plated through holes which have a plating 313 formed of amaterial such as copper optionally overcoated with gold. Because of theoffset provided between each pair of holes 306 and 307 there is provideda planar shoulder 306 in the bottom of each of the holes 306 and 307 onwhich the plating 313 is provided. The shoulders 316 with the plating313 thereon form areas to which compliant contact structures 121 of thetype hereinbefore described and as shown in FIG. 2 can be formed. Thematerial forming the shells 131 of such contact structures also extendsover the plating 313 provided for plating through the composite hole 312to form an excellent bond between the contact structure 121 and theplating 313.

It can be seen from FIG. 19 that the contact structures have a suitablelength such that their free ends extend beyond the planar surfaces 303and 304 on opposite sides of the substrate 302 so they can make contactwith electronic components as hereinafter described. The free ends ofthe interconnect structures 121 can be spaced a suitable distance apartas for example 10 to 200 mils and preferably between 20 and 100 mils.The substrate 302 can be formed of various types of plastics. Forexample they also can be polyetherimide, polysulfone or liquid crystalpolymer based plastic molded materials.

In the arrangement shown in FIG. 19, the pairs of electrodes areelectrically isolated from each other. However, it is apparent that thepairs of electrodes can be interconnected if that is desired merely byplacing conductive portions of the plating 313 on the sides or surfaces303 and 304 to make the appropriate interconnections. For example, thecommon plated portions on the surfaces 303 and 304 can represent powerand ground planes which make appropriate interconnections to power andground contacts.

In FIG. 20 there is shown a double-sided interposer 321 which consistsof a plastic substrate 322 in the form of a thin plastic sheet formed ofa suitable material such as a polyimide. A plurality of spaced apartholes 323 can be drilled or molded into the substrate 322. The substratealso can be in the form of a reinforced epoxy laminate such as an epoxyreinforced with fiberglass and the holes 323 drilled therethrough.Plating 324 of a type hereinbefore described is used for plating throughthe holes 323 and for providing metallization 326 on the top side andmetallization 327 on the bottom side of the substrate 322 as shown inFIG. 20. However in connection with the present invention, it can beseen that if desired the metallization 327 provided on the bottom sideof the substrate 322 can be eliminated if desired. A contact Structure201 like that disclosed in FIG. 13 can be mounted on the conductivelayer 326 adjacent the plated-through hole 323. This contact structure201 includes a contact structure 121 which extends resiliently from theone side of the substrate 322 whereas the other contact structure 201extends through the hole 323 and beyond the other side so a probe typecontact is available from that side. It can be seen that if desired,circuitry can be provided on the substrate 322 and connected to thecontact structures 121 and 201. In addition, pins (not shown) can beprovided in the substrate 322 for registering the interposer 321 withother electronic components as hereinafter described.

Another interposer 331 incorporating the present invention shown in FIG.21 in which resilient contact structures 121 are provided on one side ofa substrate 332 and solderable contacts 334 are provided on the oppositeside. Plated-through holes or vertical via conductors 336 are providedin the substrate 332. Standoffs 161 of the type hereinbefore describedin conjunction with FIG. 7 are provided on the opposite side of thesubstrate 332 and are connected to the plating 337 upon which thecontact structures 121 and the standoffs 161 are mounted. Thus it can beseen that the interposer 331 provides the capability of making springcontacts from one side of the interposer and solder standoffs orsolderable contacts from the other side of the interposer.

In FIG. 22 there i6 shown interposer 341 which is provided withdouble-sided resilient contact structures 121 which are disposed onopposite sides of a substrate 342 having plated through holes 343therein and the standoffs 346. The standoffs 346 are loop-shaped and aremounted on the metallization 347 carried by the substrate 342 and can bepositioned anywhere on the substrate 342. As can be seen from FIG. 22,the standoffs 346 have a height which is less than the height of thecontact structure 121 so that in the event there is undue pressureapplied by the electronic component making contact to the contactstructure 121, compressive inward movement against the yieldable forceof the contact structure 121 will be arrested by the standoffs 346. Thestandoffs 346 can be made in the same way as the contact structures 121hereinbefore described with a skeleton covered by a shell. However, itshould be appreciated that the bonds at both ends of the flexibleelongate element internal of the standoffs can be wedge bonded ifdesired.

In FIG. 23 there is shown an active semiconductor device assembly 351incorporating the present invention. Assembly 351 includes asemiconductor device 352 in the form of a silicon body which isconstructed in a manner well known to those skilled in the art and hasinternal metallization layers and internal connections. It is providedwith a top aluminum alloy metallization 353 which is covered by apassivation layer 354. A plurality of contact structures 355 of the typehereinbefore described extend through holes 356 provided in thepassivation layer 354 and make contact with the aluminum metallization353. As can be seen in FIG. 23, the uppermost tip of the contactstructures 355 are aligned in two rows with alternate contact structures355 in each row being offset from the uppermost tip of the other contactstructures 355 to provide a staggered arrangement making possible threedimensional fan-outs. The spacing between the aluminum pads on thesemiconductor device 352 may be a certain distance apart as representedby the letter D which by way of example can be 5 mils. The staggeredfree extremities of the contact structures 355 can be a much greaterdistance apart represented by mD as shown in FIG. 23 which by way ofexample could be 10 mils or 15 mils. This different spacing for the freeends is readily achieved by providing different offsets for the freeends of the contact structures 355. Thus one set of contact structures355 consisting of alternate contact structures 355 can be provided witha larger bend than the other contact structures 121 in the row so thatthe free ends of the contact structures 121 are offset by a desiredamount. In this way, it can be seen that there can be a relatively closegeometries provided on a semiconductor device with larger padseparations being possible for interconnection to another device.

If desired, an optional encapsulant 357 (see FIG. 23) can be providedwhich extends over the base of the contact structures 355 and whichextends over the surface of the semiconductor device 352 overlying thepassivation layer 354. Also, if desired, encapsulant 357 additionallycan be provided on the lower extremities of the contact structures 355as shown in FIG. 23 which serves to envelop the lower portion of thecantilever of the contact structure 355. If desired, all of the contactstructure 355 can be provided with such additional encapsulant 357. Theapplied encapsulant 357 assists in preventing or at least limitinghandling damage to semiconductor devices during assembly operations.

A semiconductor device assembly 366 incorporating another embodiment ofthe invention is shown in FIG. 24 and includes an active semiconductordevice 367 which is provided with aluminum metallization forming contactpads or areas 368. By way of example, the active semiconductor devicecan be a memory chip or microprocessor. Most of the surface of thesemiconductor device 367 is covered by a passivation layer 369. Holes oropenings 371 are formed in the passivation layer 369 in a manner wellknown to those skilled in the art as for example by utilizing aphotoresist and a suitable etch. After the holes 371 have been formed, acontinuous shorting layer (not shown) is deposited over the passivationlayer 369 and over the aluminum alloy contact pads 368. This is followedby a photoresist layer (not shown) after which holes (not shown) areformed in the photoresist which are in registration with the holes 371and are of a greater diameter by 0.5 to 5 mils and preferably 1-3 mils.Thereafter, metallization 376 in the form of a suitable material such asa layer of nickel followed by a layer of gold is formed in the holes 371and into the larger holes formed in the photoresist after which thephotoresist is stripped in a conventional manner so that there remainsthe metallization 376, and the shorting layer is etched away, other thanin the areas underneath the metallization 376. As shown in FIG. 24 themetallization is deposited to a thickness of 1-3 mils and provides anannular overhang portion 376 a.

Contact structures 381 similar to the contact structures 121 areprovided in the cup-shaped metallization 376 as shown with the flexibleelongate member or skeleton 382 being ball-bonded to the cup shapedmetallization 376 and with the shell 383 extending over the top of theannular overhang 376 to in effect provide a larger diameter cap.Alternatively, the contact structures 381 can be constructed in theholes 371 by bonding the skeletons in the holes followed by depositionof the shell or muscle, after which the photoresist can be stripped andthe shorting metal layer is etched away.

As shown in FIG. 24, the contact structures 381 can have differentconfigurations with some having larger bends and others having smallerbends with those with larger bends having longer cantilevered portions.Every other one of the contact structures 381 extend in an oppositedirection so that the free standing ends have a pitch or spacing betweenadjacent free standing ends identified as mD which is different from thepitch or dimension D between adjacent contact structures 381 at the caps376. It can be seen that by providing different angulation for thecontact structures 381 as well as providing different shapes, the freestanding ends can be disposed in a plane which is parallel to the planeof the active semiconductor device 367 but in which the spacing betweenthe free ends can be significantly different from the spacing betweenindividual contact structures at the bases of the contact structures toprovide the desired spacing or pitches at the free standing ends. Inother words, it can be seen from the semiconductor device assembly inFIG. 24 that it is possible to place contacts on a semiconductor deviceat a certain pitch whereas the same pitch or different pitches can beprovided at the free upstanding ends of the contact structures providedthereon.

It is also shown in FIG. 24 in order to facilitate alignment of thesemiconductor device assembly 366 with other electronic components asfor example printed circuit boards and the like, alignment pins 386 canbe provided which can be formed at the same time that the contactstructures 381 are formed. Thus, although in FIG. 24 a single alignmentpin 386 is shown, it should be appreciated that a plurality of suchalignment pins can be provided on a semiconductor device assembly 366.In order to facilitate the formation of such alignment pins 386 when themetallization 376 is provided on the passivation layer 369, pads 387 ofthe metallization disposed in appropriate places are provided, typicallyplaced on the passivation layer 369. The alignment pins 386 are thenformed of a skeleton 388 and a shell 389 at the same time that the othercontact structures 381 are formed. Thus it can be seen that it is veryeasy to provide the desired number of alignment pins in conjunction withthe contact structures 381 without any substantial increase in cost ofthe completed semiconductor device assembly 366.

The active semiconductor devices 367 are typically made in a wafer formas for example 8″ in diameter and with the wafers having a thicknessranging from 15 to 30 mils preferably from 15 to 25 mils although thereis the capability of providing semiconductor device assemblies as thinas 10 mils. With the construction shown in FIG. 24, it is impossible toprovide resilient contact structures 381 which can overhang the edge orouter boundary of such individual chip on a wafer so that it is possibleto make contact to the semiconductor devices in the wafer prior to diecutting a wafer. This die cutting or dicing operation is typicallydescribed as singulation in which the wafer is cut into singlesemiconductor devices. In connection with the design of thesemiconductor device assembly 366, it is desirable that the contactstructures 381 be positioned in a manner shown in FIG. 23 so that aminimum surface area is required for die cutting to provide the desiredsingulation. Typically these regions in which the cutting is to takeplace are called scribe streets. By alternating the contact structures381 provided on those pads to provide the offsets as shown in FIG. 24 itis possible to obtain increased pitches for making interconnections toother electronic components.

Thus it can be seen that the process of the present invention can beutilized with semiconductor devices in wafer form as well as with singlesemiconductor devices. Also with the arrangement shown in FIG. 24 it canbe seen that interconnections can be made with the contact structures381 at the same time that the alignment pins 386 are being utilized toachieve the proper alignment for the contact structures and theelectronic component being mated therewith.

A semiconductor device assembly 366 of the type shown in FIG. 24 iscapable of being tested at its full functional speed by yieldably urgingthe tips of the contact structures 381 into compressive engagement withmatching contact terminals provided on a test substrate (not shown).Such testing can be carried out without the need of special probescarried by a test substrate. In order to ensure excellent contactbetween the contact terminals on the test substrate, the conductiveshell 383 can be provided with an outer layer of a noble metal such asgold, rhodium or silver by providing a similar material on the contactpads of the test substrate, a low contact resistance is obtained.Heretofore it has been necessary for test probes to engage typicallyaluminum contacts which have a propensity to oxidize, resulting in highcontact resistance.

The construction shown in FIG. 24, in addition to facilitating testprocedures, can also be utilized for burn-in testing of thesemiconductor device. Thus, in the same manner, the semiconductor deviceassembly 367 can have its contact structures 381 yieldably engagematching contact pads provided on a burn-in test substrate (not shown)which can be formed of the same material as the contact pads provided onthe test substrate. The device 367 when in contact with the burn-in testsubstrate can be exercised during prolonged periods while being exposedto alternately high and low temperatures. In connection with suchburn-in testing, it should be appreciated that multiple semiconductordevices 367 can be used to populate a burn-in board or substrate capableof receiving a plurality of such semiconductor devices 367 and retainedin engagement therewith by spring clips of the types hereinafterdescribed in connection with FIGS. 26 and 27. Registration of thesemiconductor device assembly 367 with the test burn-in substrates canbe facilitated by the use of the registration or alignment pins 386. Thefan-out capabilities provided with the semiconductor structures 381arranged in the manner shown in FIG. 24 makes it possible to have a finepitch for the contact pads on the semiconductor device assembly 367 witha coarser pitch for the tips of the contact structures 381. This makesit possible to simplify the registration of such semiconductor deviceswith coarser and possibly a standard pitch for the contact pads on thetest and burn-in substrates, making it possible to reduce the cost ofsuch test and burn-in substrates.

After the testing and burn-in procedures have been performed on thesemiconductor devices 367 and the performance of the devices has beenvalidated, they can be removed from the test and/or burn-in substratesby removing the spring clips and thereafter bringing the free ends ofthe contact structures 381 into engagement with matching patterns ofcontact pads provided on an interconnection substrate of the typehereinafter described to provide a permanent interconnection. Thefan-out capabilities of the contact structures 381 shown in FIG. 24 alsomake it possible to utilize a pitch on the contact pads carried by theinterconnection substrate which differs from the pitch of the contactpads on the semiconductor device 367. The registration pins 386 can alsoaid in making the desired registration and simplifies making thepermanent interconnections.

A semiconductor package assembly 401 is shown in FIG. 25. Mounted withinthe package assembly 401 is a printed circuit (PC) board 411 whichcarries circuitry which includes contact pads 412 on one side of theprinted circuit board 411 and additional contact pads 413 on the otherside of the PC board. Semiconductor devices 416 and 417 are provided onopposite sides of the printed circuit board and carry resilient contactstructures 418 that are mounted thereon in a manner hereinbeforedescribed to provide a double-sided flip chip attachment to the circuitboard 411 with solderable terminals. The resilient contact structures418 are bonded to the contact pads 412 and 413 by passing the assemblythrough a suitable furnace to cause the solder carried by the resilientcontact structures 418 to form a solder joint with the contact pads 412and 413. This process can be further assisted by the use of reflowablesolder paste applied to contact pads 412 and 413, as is well known tothose skilled in the art of surface mount assembly technologies. Anencapsulant 419 formed of a suitable insulating material is disposedbetween the printed circuit board 411 and the semiconductor devices 416and 417 to complete the package.

Another semiconductor package assembly 421 incorporating the presentinvention is shown in FIG. 26 and includes a laminated printed circuitboard 423 carrying pads 424 and 426 on opposite sides of the same.Semiconductor devices 427 and 428 are disposed on opposite sides of thePC board 423 and carry contact structures 429 of the type hereinbeforedescribed. The contact structures 429 can be yieldably urged intoengagement with the contact pads 424 and 426 by spring-like clips 431which are secured to the printed circuit board and which snap over theedges of the semiconductor devices 427 and 428. These spring-like clips431 can be dispersed around the perimeter of the semiconductor devicesas for example for a rectangular semiconductor device at least four ofsuch spring-like clips 431 can be provided with two on each of twoopposite sides. The spring clips 431 as shown are bonded to contact pads432 carried by the printed circuit board 423. Each of the clips 431 isprovided with a flexible elongate element or skeleton 433 of the typehereinbefore described which is bonded in a suitable manner as forexample by a ball bond to the pads 433. The skeleton 433 is providedwith two bends 433 a and 433 b to form the spring-like clip whichextends over one side of the semiconductor device as shown in FIG. 27. Ashell 434 provides a suitable reinforcement or muscle for the clips 431and augments the spring-like or clip-like characteristics of the bends433 a and 433 b to retain the semiconductor devices 427 and 428 inplace. With such an arrangement, it can be seen that the semiconductordevices 427 and 428 with their contact structures 429 are retained inintimate contact with the contact pads 424 and 426. This arrangementpermits registration of contact structures 429 with the contact pads 424and 426. When it is desired to remove the semiconductor devices 427 and428, it is only necessary to push the spring clips 431 outwardly torelease the semiconductor devices 427 and 428 carrying with them thecontact structures 429 which become disengaged from the contact pads 424and 426.

A solder coating can be provided either on the free ends of the contactstructures or on the contact pads to be engaged thereby and by thenpassing the assembly through a furnace, the solder forms a joint masswhich intimately encompasses the free ends of the contact structures andthe surfaces of the pads leaving only an optional thin coating on thelengths of the contact structures to thereby provide a connection whichis compliant in three directions, X, Y and Z directions.

An alternative semiconductor package assembly 441 is shown in FIG. 27and includes a PC board 442 or other suitable substrate which carriescontact pads 443 and 444 that are spaced apart on one surface of the PCboard 442. Contact structures 446 are mounted on the pads 443 and arecomprised of a skeleton 447 and shell 448 construction in the mannershown to provide a resilient contact structure. Spring clips 451 of thetype shown in FIG. 26 are secured to the pads 444. As shown in FIG. 27 asemiconductor device 452 is clamped between the uppermost extremities ofthe contact structures 446 and removably engages metallized cup-shapedterminals 453 carried by the semiconductor device 452 of a typehereinbefore described. In this construction it can be seen that thesemiconductor device 452 is demountable by merely pushing aside thespring clips 451 because there is no solder interconnection between thedistal or free extremities of the contact structures 446 and the contactterminals 453 carried by the semiconductor device 452. It should beappreciated with the arrangement shown in FIG. 27 that if desired, thecontact structures 446 can be mounted in the wells 453 carried by thesemiconductor device 452 and that the free ends of the contactstructures 446 removably engage the pads 443 carried by the printedcircuit board and to thereby achieve substantially the same results asachieved by the arrangement shown in FIG. 27. It should be appreciatedthat in place of spring clips 451, external spring elements (not shown)can be used to spring load the contact structures 446 against metallizedwells 453.

Another semiconductor package 461 is shown in FIG. 28 which isparticularly suited for use with printed circuit boards 462 havingvertical via conductors or plated-through holes 463 extendingtherethrough. A semiconductor device 466 is provided which carriesresilient contact structures 467 of a type hereinbefore described. Thecontact structures 467 as shown are provided with a plurality of bends467 a and 467 b particularly at their free ends which bends are such sothat they subtend a diameter which is greater than the diameter of theplated through holes 463 provided in the printed circuit board. Thus asshown in FIG. 28, when the semiconductor device is positioned so thatthe contact structures 467 are in registration with the plated throughholes, the contact structures 467 can be pushed into the plated throughholes to form spring-loaded fits between the contact structures 467 andthe walls of the plated-through holes 463 to retain the semiconductordevice 466 in a demountable or removably mounted position on the PCboard 462 and making electrical contact with the plated-through holes sothat contact can be made from the printed circuit board to the outsideworld.

Still another semiconductor package assembly 471 incorporating thepresent invention is shown in FIG. 29 in which there is provided a PCboard 472 having a plurality of spaced apart holes 473 provided therein.Spaced apart contact pads 476 are provided on opposite sides of the PCboard. Semiconductor devices 477 and 478 are provided on opposite sidesand carry contact structures 481 of the type hereinbefore describedwhich are of a resilient type and have free ends which are adapted toengage the contact pads 476. Spring clips 486 of the type alsohereinbefore described are mounted on the semiconductor device in amanner hereinbefore described and are positioned on the semiconductordevice so that they are in registration with the holes 473 provided inthe printed circuit board 472. As shown, the semiconductor devices 477and 478 can be clipped to the PC board 472 by having the spring clips486 extend through the holes 473 and having portions 486 a engaging theopposite sides of the printed circuit board as shown in FIG. 29. In thisconnection, a solder connection can optionally be formed between thefree ends of the contact structures 481 and the contact pads 476.Alternatively as hereinbefore described, the free ends can be formed sothat they can make a removable resilient contact with the pads 476. Sucha construction can be readily made by providing free ends which areadapted to frictionally engage the contact pads 476 through springloading.

Another semiconductor package assembly 491 is shown in FIG. 30incorporating another embodiment of the invention in which a PC board492 is provided having spaced apart holes 493 extending therethrough.Semiconductor devices 494 and 496 of the type hereinbefore described areprovided and have mounted thereon contact structures 497. Similarlyalignment pins 498 of the type hereinbefore described are mounted on thesemiconductor devices 494 and 496.

In assembling the semiconductor package assembly 491, the semiconductordevice 496 which can be in the form of a semiconductor chip which can beplaced on a carrier (not shown) for automated handling after which thechips are selected and brought over the top with the holes 493 inregistration with the alignment pins 498. Thereafter as shown, the upperextremities of the alignment pins 498 are bent over to retain theprinted circuit board in engagement with the semiconductor device 496.This intermediate assembly of the semiconductor device 496 and printedcircuit 492 is flipped. Thereafter, the second semiconductor device 494is brought over the top of the printed circuit board 492 and turnedupside down so that the alignment pins 498 are in alignment with otherholes 493 in a printed circuit board and then moved into the holes 493to cause the contact structures 497 carried thereby to move intoengagement with the contact pads 499 on the printed circuit board. Inorder to additionally assist retaining the parts in an alignedcondition, an adhesive 501 of a suitable type, with an appropriatesolvent which shrinks upon curing due to solvent evaporation can beoptionally placed between the printed circuit board 492 and thesemiconductor devices 494. It can be seen that if desired when anadhesive is used, the free extremities of the alignment pins 498 carriedby the semiconductor device 496 need not be bent over as shown.

Another semiconductor package assembly 506 incorporating the presentinvention as shown in FIG. 31 includes a printed circuit board 507 whichis provided with a large plated through opening or hole 508. A capacitor511 is disposed in the large plated through hole 508 and includes firstand second electrode plates 512 and 513 separated by dielectric material514. The free extension 512 a of the plate 512 is bonded to the portion508 a of the plating for the plated through hole 508 and the freeextension 513 a of the other plate 513 is bonded to the plating portion508 b of the plating for the plated through hole 508. In this way it canbe seen that the capacitor 511 is suspended in the plated through hole508. A plurality of contact pads 516 are provided on the upper and lowersurfaces of the substrate or the PC board 507 and are spaced apart fromthe plated through hole 508. Another contact pad 517 is provided on theprinted circuit board and is in contact with the portion 508 b of theplated through hole 508. Semiconductor devices 521 and 522 are providedand are of a type hereinbefore described and carry contact structures523 of the type hereinbefore described which are soldered to the contactpads 516 and the contact pads 517 as shown.

Another semiconductor device assembly 526 incorporating the presentinvention is shown in FIG. 32 and includes a PC board 527 which carriesa plurality of spaced apart contact pads 528 on opposite sides of thesame which are bonded to contact structures 529 of the resilient typehereinbefore described which are mounted on semiconductor devices 531and 532. Capacitors 511 of the type hereinbefore described are disposedon opposite sides of the printed circuit board 527. The capacitors 511are provided with plates 512 and 513 which are bonded to contact pads533 provided on opposite sides of the printed circuit board 527. Thus itcan be seen that the capacitors 511 are disposed in the spaces betweenthe semiconductor devices 531 and 532 and opposite sides of the printedcircuit board 527. There is adequate space for such capacitors as neededin connection with the semiconductor devices 531 and 532. It can be seenby adjusting the height of the resilient contact structures 529 thatadequate space can be provided for the capacitors 511 and between theprinted circuit board and the printed circuit board 527 and thesemiconductor devices 531 and 532.

Another semiconductor device assembly 536 incorporating the presentinvention is shown in FIG. 33 and as shown therein includes a multilayerprinted circuit board or substrate 537 which is provided with first andsecond surfaces 538 and 539. A rectangular recess of 541 is provided inthe PC board 537 which opens through the first surface 538. A pluralityof spaced apart steps 542 are provided accessible through the sidehaving a surface 539 thereon and are at various elevations with respectto the surface 539 so as in effect to form depressions or recessessurface 539. As shown, the printed circuit board 537 is provided with atleast three different levels of metallization identified as 546. It isalso provided with a plurality of vertical via conductors or verticalvias 549 which as shown extend in directions perpendicular to thesurfaces 538 and 539 and make various interconnections as shown in FIG.33. The vertical vias 559 can be formed of a suitable material such asmolybdenum or tungsten in a ceramic substrate or in the form ofplated-through holes in laminated printed circuit boards. A plurality ofcontact pads 551 are provided in the side carrying the second surface539 and as shown are disposed on the steps 542 as well as on the surface539 and are thereby directly connected to several levels ofmetallization. Resilient contact structures 552 of the type hereinbeforedescribed are bonded to each of the contact pads 551 and are of variouslengths as shown in FIG. 33 so that their free extremities substantiallylie in a single plane which is generally parallel to the surface 539 andthe surfaces of the steps 542.

A through-hole decoupling capacitor 556 is provided which is comprisedof multiple capacitors formed by a plurality of parallel conductingplates 557 disposed in a dielectric material 558 of a type well known tothose skilled in the art. The plates 557 are connected to vertical vias559. The vertical vias 559 on one side are connected to contact pads 561which are disposed within the recess 541 and make contact with thevertical vias 549 carried by the printed circuit board 537.

As can be seen in FIG. 33, the upper surface of the decoupling capacitor556 just extends slightly above the surface 538 of the printed circuitboard 537. Metallization is provided on the surface 538 of the printedcircuit board and provides contact pads 562. Additional contact pads 563are provided on the decoupling capacitor 556 which are in contact withthe vertical vias 559. A semiconductor device or chip 566 is providedwhich has a plurality of contact pads 567. Resilient contact structures568 of the type herein described are mounted on the contact pads 562 and563 with the uppermost points of the contacts 568 terminatingsubstantially in common horizontal plane so that the free ends of thecontact structures 568 are bonded to the contact pads 567 on theintegrated semiconductor device 566. Thus it can be seen that theresilient contact structures 568 readily accommodate the disparity inthe levels of the planar surfaces of the decoupling capacitor 556 andthe surface 538 of the printed circuit board 537. This makes it possibleto bond the planar surface of a chip 566 to surfaces which may not beplanar as shown in FIG. 33.

This type of construction makes it possible to provide very lowinductance coupling to the decoupling capacitor 556 which is a veryimportant parameter defining the performance of a microprocessor. Asexplained previously, all of the contacts on the other side of theprinted circuit board 537 do not originate in the same plane whichfacilitates making direct connections to the contact pads on thedifferent planes as shown. This makes it possible to reduce the numberof vias and conductors required for interconnections within thesubstrate.

Although the final outside packaging for the semiconductor packageassembly 536 is not shown, it can be readily appreciated by thoseskilled in the art, packaging of the type hereinbefore described can beutilized.

Alternatively, the under chip 566 which is shown in FIG. 33 can beencapsulated (not shown) in a suitable polymer or epoxy based compound.

It should be appreciated that if desired, the printed circuit board 537can be on a larger scale 80 that it can accommodate severalsemiconductor face-down connected chips on the surface 538 by utilizingthe same principles which are shown in FIG. 33. Thus flip chips 566 canbe provided adjacent to each other arranged in rows extending in boththe X and the Y directions as desired.

Another semiconductor package assembly 571 incorporating the presentinvention is shown in FIG. 34 and as shown therein is in a form of acomposite structure which by way of example can include a semiconductorpackage assembly 536 of the type hereinbefore described in conjunctionwith FIG. 33 showing the way that it can be mounted on another printedcircuit board 576 which can be characterized as a motherboard or anintegration substrate. As shown, the motherboard 576 is provided withfirst and second surfaces 577 and 578 provided by solder layers 579,often called solder masks, disposed on opposite sides of the motherboard576. The motherboard also has multiple layers of metallization 581 and aplurality of spaced-apart vertical plated-through holes 583 extendingperpendicular to the surfaces 577 and 578. The plated-through holes 583are provided with contact surfaces 586 which are accessible throughopenings 587 provided in the surface 577. They are also provided withcontact surfaces 591 accessible through holes 592 in the layer 579 whichextend through to the surface 578. As shown in FIG. 34, the contactsurfaces 586 are engaged by the free extremities of the resilientcontact structures 552 and are bonded thereto by suitable means such asa solder or an electrically conductive epoxy to complete the assembly.

It should be appreciated that with a large motherboard a plurality ofsemiconductor package assemblies 536 of the type shown in FIG. 33 can bemounted on the same other printed circuit board or integrationsubstrate. Similarly, semiconductor package assemblies 536 can becounted on the other side of the mother printed circuit board which areprepared in a manner similar to that hereinbefore described.

In connection with mounting the semiconductor package assembly 536 on amother circuit board, rather than the direct solder contacts shown inFIG. 34, it should be appreciated that if desired, the contactstructures 552 can be in the form of demountable contact structures suchas the contact structures 467 shown in FIG. 28 to make electrical andspring-loaded contact with the conductive terminals connected toplated-through holes 583 provided in the motherboard. Thus in thismanner, spring loaded fits can be provided between the motherboard 576and the semiconductor package assembly 536. Such a construction isdesirable because it makes it possible to replace a semiconductorpackage in the field. Thus, for example by utilizing such spring loadedcontacts, the semiconductor package assembly 536 can be removed andreplaced by another one of greater capabilities. For example, amicroprocessor in a notebook computer could be upgraded in this manner.In this case, a methodology for the use of integrated resilient contactsincludes burn-in and tect of the assembly 536 by engaging the resilientcontacts against pads on an appropriate test or burn-in substrate andthen spring loading the component to the board 576 as heretoforedescribed.

Another composite semiconductor package assembly 601 incorporating thepresent invention is shown in FIG. 35 end shows a printed circuit board537 with the semiconductor device 566 mounted thereon and with a motherprinted circuit board 576 of the type hereinbefore described with aninterposer 602 of the type shown in FIG. 21 being utilized between theprinted circuit board 537 and the mother printed circuit board 576 withsolder 603 being utilized for bonding the contact structures 161 of theinterposer 602 to the contact surfaces 586. Similarly, the contactstructures 121 of the interposer 602 are yieldably retained inengagement with the contact pads 551 and are retained in engagementtherewith by suitable means such as through bolts 606 provided with nuts607 extending through the printed circuit board 537 and through themother circuit board 576 and through the interposer 602 to form acomposite assembly in which the compression on the contact structures121 is maintained to provide good electrical contact with the contactpads 551 carried by the printed circuit board 537.

In place of the bolts 606 it should be appreciated that other fasteningmeans can be utilized as for example spring clips to retain thecompression on the contact structures 121 and to fasten the printedcircuit boards together as hereinbefore described. Rather than theinterposer 602 being formed as an interposer of the type shown in FIG.21, an interposer of the type shown in FIG. 20 can be utilized withremovable electrode contacts being formed on both sides of theinterposer and by having the contact structures 121 yieldably engage thecontact pads 551 and having the contact structures 201 yieldably engagethe surfaces 586. With such a construction it can be seen that changescan be readily made in a composite semiconductor package assembly merelyby removing the bolts and replacing certain other components as well asthe interposer if desired. The interposer is demountable to facilitatesuch changes.

Another semiconductor package assembly incorporating the presentinvention is shown in FIG. 36. The assembly 611 discloses the manner inwhich packing of silicon on cards can be obtained and includes aninterconnection substrate 612 formed of a suitable insulating materialwhich is provided with first and second surfaces 613 and 614. Such aninterconnecting substrate can be of the type of the printed circuitboards hereinbefore described and for example can contain a plurality oflevels of metallization (not shown) as well as through-hole conductorsor via conductors 616 which are in contact with contact pads 617provided on the surfaces 613 and 614.

Semiconductor devices in the form of face-down mounted chips 621 areprovided which are adapted to be disposed on opposite sides of theinterconnection substrate 612. As described in connection with theprevious semiconductor devices, these devices are provided with aplurality of contact pads 622 which have a resilient contact structures626 of the type hereinbefore described mounted thereon and which areturned upside down to make electrical contact to the contact pads 617provided on the interconnection substrate 612. The space between theflip chips 621 and the interconnection substrate 612 can be filled witha suitable encapsulant 631 as shown.

All of the electrical connections are provided within the various flipchips can be brought out to a plurality of contacts 636 provided on oneedge of the assembly 611 as shown in FIG. 36 serve as precursors and sothat the semiconductor package assembly 611 can be fitted intoconventional sockets for example as provided in a desktop computer andthe like. With such a construction, it can be seen that silicon chipscan be face down mounted on both sides of the interconnection substrate612.

Another semiconductor package assembly 651 incorporating the presentinvention is shown in FIG. 37 and shows the manner in which thesemiconductor package assembly 611 shown in FIG. 36 can be verticallystacked with the device semiconductor package assembly 611 beingdescribed as a double stacked card. As shown in FIG. 37 two of thesedouble-sided silicon precursors have been mounted vertically withrespect to each other with additional contact structures 652 havinginterconnections between the two interconnection substrates 612 of theprecursors 611. The entire assembly can be optionally encapsulated witha polymeric or epoxy material for added rigidity and protection.

Another semiconductor package assembly 661 incorporating the presentinvention is shown in FIG. 38. It shows an assembly 661 in which asubstrate 662 of the type hereinbefore described can be provided, as forexample a printed circuit board made of a plastic/laminate or ceramic orsilicon with the substrate 662 lying in a plane. A plurality of siliconchips or semiconductor devices 663 are stacked vertically inspaced-apart positions on the substrate 662 and extend in a directiongenerally perpendicular to the plane of the substrate 662. The substrate662 is provided with a planar surface 666 which has contact pads 667connected to circuitry in the substrate 662. Similarly, the siliconchips 663 are provided with parallel spaced-apart surfaces 668 and 669with contacts 671 being exposed through the surface 668. Contactstructures 672 of the type hereinbefore described are provided formaking contacts between the contacts 671 of the silicon semiconductordevices 663 and the pads 667 carried by the substrate 662. Thus asshown, a contact structure 672 is provided for each of the silicon chips663. The contact structures 672 can be of a resilient type and areprovided with bends 672 a.

Additional contact structures 676 have been provided of the resilienttype and are provided with first and second bends 676 a and 676 b. Thebends 676 a and 676 b are sized in such a manner so that when a contactstructure 676 is secured to another pad 678 provided on the surface 666of the substrate 662, they will engage opposite surfaces of the siliconchip 663 to resiliently support the chip 663 in their vertical positionswith respect to the substrate 662.

In connection with the foregoing, it should be appreciated that in placeof the single contact structure 676 between each pair of silicon chips,it is possible to provide two separate resilient contact structures withone facing in one direction and the other in the opposite direction toprovide the same support as is provided by the single resilient contactstructure.

From the foregoing it can be seen that the semiconductor packageassembly 661 shown in FIG. 38 lends itself to mass production techniquesas for example for stacking memory chips.

In connection with the description of the interconnecting contactstructures, interposers and semiconductor assemblies and packages, themethods utilized in fabricating the same have been generally described.The flexible elongate elements, as for example, 106 serving as theskeletons for the contact structures and used as interconnects can beformed utilizing automated wire bonding equipment which is designed toenable bonding of wires using ultrasonic, thermal or compression energyor a combination thereof utilizing such equipment to provide a wirehaving a continuous feed end and then intimately bonding the feed end toa contact pad or terminal by a combination of thermacompression orultrasonic energy and thereafter forming from the bonded free end a pinor item which protrudes from the terminal and has a first item end. Ifdesired, the second stem end can be bonded to the same contact pad orterminal or to a different contact pad or terminal. The pin or item canthen be severed at the second stem end to define a skeleton. Thereafter,a conductive material is deposited on the skeleton to form a shell ashereinbefore described and on an immediately adjacent area of thecontact pad or terminal. This procedure can be replicated to provideadditional contact structures.

These are basic steps in the present method for forming the contactstructures for making interconnections as hereinbefore described, whichalso can be characterized is forming protuberant conductive contacts.These contact structures or protuberant conductive contacts can beincorporated into and utilized in conjunction with many conventionalsemiconductor processes for fabricating semiconductor wafers. Ashereinbefore explained, chip passivation utilizing oxide, nitride orpolymer dielectric layers can be provided. In addition, shorting layersof s suitable material such as an aluminum, copper, titanium, tungsten,gold or a combination thereof can be utilized. Such a shorting layermakes it possible to use wire bonding equipment which uses high voltagedischarge for the severing operations. The shorting layer, optionallyelectrically grounded, prevents possible damage to the activesemiconductor device. Typically, such a shorting layer can be providedand overcoated with a resist and then the skeletons are mounted on thecontact pads, defined by the openings in the resist. The skeletons thenare overplated with a conductive material to form the shell or muscle,after which the resist and shorting layer can be removed as hereinbeforedescribed. The wafers can Thereafter, the diced chips then be singulatedor diced. can be optionally coated with a protective polymer whichextends over the region in which the bonds are made to the contact pad.

In connection with such a method, the openings in the resist can be madeof a larger size than that of the contact pads. Thereafter, metal can beplated up through the opening in the resist to provide a larger sizecontact pad or well. The resist and the shorting layer can then beremoved, except underneath the larger area contact pad provided.

By providing such a larger area for the contact pad, there is a greatersurface to promote adhesion to the contact structures fabricated inaccordance with the present invention. Such augmented contact pads canbe of any desired shape, such as circular, oval, rectangular and thelike. The plated-up metal contact pads have an additional advantage inthat they serve to hermetically seal the typically aluminum contact padsfrom the atmosphere.

Heretofore a method was described in which a contact pad was providedfor the free end of a contact structure on which a sacrificial layer wasremoved after the deposition of the overcoating muscle layer or shell.It should be appreciated that if desired the sacrificial structure canbe removed prior to deposition of the overcoating or shell and then theovercoating or shell being formed thereon with CVD, electroless platingor electroplating with a shorting layer for contact.

Also heretofore described was a method for the fabrication of aprobe-like contact structure with the use of a sacrificial member suchas aluminum or copper. Such a method also can be utilized for the gangtransfer of a plurality of contacts onto a package prior to placing thesemiconductor chip in the package. In the event of the failure of apackage, the expense of the semiconductor chip will be saved with theonly resulting loss being in the package and the contacts therein. Thusin accordance with the present invention, the plurality of contacts canbe formed on a transfer/sacrificial substrate according to any methodheretofore and thereafter gang attached to the package after which thetransfer/sacrificial substrate can be removed. The attachment of aplurality of contacts on a sacrificial substrate carrier can be readilyaccomplished by utilizing a software data file to create the requiredpattern on the transfer substrate without the use of special molds.

By the use of resilient contact structures carried by semiconductordevices as hereinbefore disclosed and using the same to make yieldableand disengageable contacts with contact pads carried by test and burn-insubstrates, testing and burn-in can be readily accomplished to ascertainthat desired performance characteristics have been met and thereafterthe same semiconductor device can be removed from the test and burn-insubstrates and without change incorporated into permanent packaging ashereinbefore described by placing multiple semiconductor devices on acommon substrate and thereby avoiding the need for first levelsemiconductor packaging. Thus, in accordance with the present invention,the active semiconductor device can be tested when it is unpackaged andalso after it has been packaged into permanent package assembly.

From the foregoing, it can be seen that there has been provided acontact structure for making interconnections with interposers,semiconductor assemblies and packages using the same and a method forfabricating the same. As hereinbefore described, the contact structurehas great versatility and can be utilized in many different applicationsin the semiconductor industry to facilitate mass production ofsemiconductor assemblies and packages. The contact structures provideincreased reliability and high structural integrity making thesemiconductor assemblies and packages incorporating the same capable ofbeing utilized in rather adverse environments. Because of theversatility and resiliency of the contact structures of the presentinvention, it is possible to use the same in many differentsemiconductor assemblies and package configurations with the contactsbeing made at different elevations and with different pitches. Thecontact structure can be utilized in many different configurations forthe pads permitting the mounting of semiconductor chips on SIMM andother cards. The contact structures and methods herein disclosed make itpossible to fabricate card-ready devices with directly mounted resilientcontacts. The method is suitable for mounting contact semiconductordevices either in wafer or singulated form. The equipment utilized forperforming the method utilizes micromechanical hardware which is similarto conventional wire bonders already in use in the industry.

What is claimed is:
 1. A method of forming a resilient contact structurecomprising: mounting a portion of an elongate flexible core element to aterminal of an electronic component, the elongate flexible core elementhaving a length extending from the electronic component, the lengthhaving first and second sections, and a change in direction of thelength between the first and second sections; and then forming aconductive shell over at least the first and second sections of thelength of the elongate flexible core element, wherein; (i) theconductive shell comprises at least one layer having a material whichhas a yield strength of at least thirty thousand pounds per square inch;and (ii) the elongate flexible core element and the conductive shellbeing formed to be a free standing interconnection spring element havinga portion secured to the terminal, a contact region located distant fromthe electronic component, and an elongate section between the portionand the contact region, the elongate section having a shape which allowsthe elongate section to bend when the contact region is depressedtowards the terminal, the elongate section substantially returning to anoriginal shape due to resiliency thereof because of the yield strengthof the material of the conductive shell.
 2. The method, according toclaim 1, wherein: the core element comprises a material selected fromthe group consisting of gold, aluminum and copper with inclusions ofberyllium, cadmium, silicon and magnesium, metals of a platinum group,and lead, tin, and indium.
 3. The method, according to claim 1, wherein:the core element has a diameter in a range of from 0.25 to 10 mils. 4.The method, according to claim 1, wherein: the elongate core element hasthe length in the range of from 10 mils to 500 mils.
 5. The method,according to claim 1, wherein: the shell is formed as a multilayershell; and at least one layer of the shell is formed of a material whichis selected for the ability to provide mechanical properties selectedfrom the group consisting of spring properties, resiliency yieldstrength and compliance for the resilient contact structure.
 6. Themethod, according to claim 1, wherein: the shell is formed as amultilayer shell; and at least one layer of the shell comprises amaterial selected from the group consisting of nickel, iron, cobalt. 7.The method, according to claim 1, wherein: the shell is formed as amultilayer shell; and at least one layer of the shell comprises amaterial selected from the group consisting of copper, nickel, cobalt,tin, boron, phosphorous, chromium, tungsten, molybdenum, bismuth,indium, cesium, antimony, gold, silver, rhodium, palladium, platinum,and ruthenium.
 8. The method, according to claim 1, wherein: the shellis formed as a multilayer shell; and at least one layer of the shellcomprises a material selected from the group consisting of nickel,cobalt, iron, phosphorous, boron, copper, tungsten, molybdenum, rhodium,chromium, ruthenium, lead, and tin.
 9. A method, according to claim 1,wherein: the shell is formed as a first layer and a second layer overthe first layer and the second layer comprises a material selected fromthe group consisting of gold, silver, metals of a platinum group, andsolder.
 10. The method, according to claim 1, wherein: the shell has athickness in a range of from 0.20 mils to 20 mils.
 11. The method,according to claim 1, wherein: the shell is formed as a multilayershell; and an inner layer of the shell is in a form of a coatingselected from the group consisting of nickel and nickel alloys.
 12. Themethod, according to claim 1, wherein: the shell is formed as amultilayer shell; and an inner layer of the shell has a thickness in therange of from 1 to 3 mils.
 13. The method, according to claim 1,wherein: the shell is formed as a multilayer shell; and an inner layerof the shell is a material selected from the group consisting of copperand nickel; and an outer layer of the shell is solder.
 14. The method,according to claim 13, wherein: the outer layer has a thickness in arange of from 1 to 1.5 mils.
 15. The method, according to claim 1,wherein: the elongate flexible core element is mounted to the terminalby bonding, thereby forming a bond.
 16. The method, according to claim15, wherein: the bond is a ball-type bond connection.
 17. The method,according to claim 15, wherein: the bond is a wedge-type bond.
 18. Amethod, according to claim 15, wherein: the shell is formed onto thecore element using aqueous plating technique.
 19. The method, accordingto claim 15, wherein: the shell is formed onto the core element by aprocess selected from the group consisting of physical vapor deposition,chemical vapor deposition, decomposition processes using gaseous, liquidor solid precursors, evaporating and sputtering.
 20. The method of claim1 wherein the freestanding interconnection spring element extends fromthe terminal, whereafter the freestanding interconnection elementchanges direction at least once.
 21. The method of claim 20 wherein theelongate flexible core element extends from the terminal, whereafter theelongate flexible core element changes direction at least once, theconductive shell being formed on the elongate flexible core elementwhich changes direction at least once.
 22. A method of forming aresilient contact structure comprising: mounting a portion of elongateflexible core element to a terminal of an electronic component, theelongate flexible core element having a length extending from theelectronic component, the length having first and second sections and achange in direction of the length between the first and second section;and then forming a conductive shell over at least the first and secondsections of the length of the elongate flexible core element, wherein;(i) the conductive shell comprises at least one layer having a materialand (ii) the elongate flexible core element and the conductive shellbeing formed to be a free standing interconnection spring element havinga portion secured to the terminal, a contact region located in anoriginal position distant from the electronic component, and an elongatesection between the portion and the contact region, the elongate sectionhaving a shape which allows the elongate section to bend when thecontact region is depressed by an actuation force towards the terminal,the elongate section substantially returning to an original shape whenthe actuation force is removed from the contact region, so that thecontact portion returns to the original position.